The InfiniBand (IB) Architecture defines a computer networking architecture that allows end nodes to communicate with one another via a fabric or subnetwork comprising one or more switches. A full definition of the IB Architecture may be found in the InfiniBand Architecture Specification Volumes 1 and 2, available from the InfiniBand Trade Association (www.infiniBandta.org), which is hereby incorporated by reference.
When a new connection is powered up in a communications network it is common to perform link training. Such link training may be used to set threshold levels in physical (hardware) devices, for example in relation to signal timing and amplitude. Although the IB specification includes such link training, it does not define any elaborate link testing or diagnostics operations. As a result, it is possible for a link to train satisfactorily, but still to have certain inherent problems. In addition, the IB specification does not require a subnet manager (SM) to support any additional link testing and diagnostics, beyond being able to read diagnostic status attributes, and being able to observe error counter attributes that may be updated during training and/or normal operation.
Consequently, the default approach for handling any additional desired testing is based on manual or bespoke coordination of instructions to the controlling logic on each side of a link. This coordination is performed via some out-of-band mechanism. Such an approach has been used, for example, with the link built-in self-test (LBIST) procedures for IB nodes from Sun Microsystems. However, this is only feasible where the subnet manager is compatible with the testing and coordination between the controlling logic on the two network nodes representing the ends of the link. Otherwise, the subnet manager may regard an attempt to perform elaborate link BIST operations as a case of link failure. As a result, nodes that implement such testing are restricted to use in conjunction with a subnet manager that also supports such testing, thereby limiting interoperability and flexibility for customers in configuring an IB network.